the invention relates to a pump for simultaneously generating pressure and negative pressure.
Such pumps are advantageous if an industrial process requires compressed air and negative pressure at the same time, since the pump only needs one drive. Aside from the suction port, such a pump requires a separate charging port that is connected to the atmosphere in order to ensure the volume flow for the compressed air. Accordingly, the pump chamber has to have several cells that are separated from each other. In the state of the art, this has only been achieved with vane type pumps which are known, for example, from the GB-A-818 691. Vane type pumps, however, are prone to wear and tear, and can only be operated without lubricants when special materials are used.
The present invention provides a pump for simultaneously generating compressed air and negative pressure, that is virtually free of wear and tear and that can be made without the use of special materials. In the pump according to the invention, there is a pair of rotors in the pump chamber that has at least three blades and that rotates in opposite directions around parallel spaced axes and these rotors intermesh free of contact so that, together with the peripheral wall of the pump chamber, they define cells that are separate from each other. The cells needed for simultaneously generating compressed air and vacuum can be separated from each other by means of the rotors. Since the rotors interact free of contact with each other and with the peripheral wall of the pump chamber, no wear occurs in the area of the pump chamber. The sealing gap between the rotors can be kept very small by optimizing their geometry; in practical embodiments, the gap is just fractions of a millimeter, so that good pressure and vacuum values are ensured. These values even improve with increasing service life since the deposits that form over time reduce the size of the sealing gaps.
A pump with a pair of rotors each having three blades and rotating in opposite directions around parallel axes is known from the DE-A-2 422 857. That pump is not equipped, however, with a charging port and is therefore not suited for producing compressed air and negative pressure at the same time.
The pump according to the invention is particularly well suited for use in the paper-processing industry, especially for applications that do not require a separate supply or adjustment of compressed air and vacuum. Compressed air is needed, for example, to blow air onto a stack of paper from the side to help separate the sheets. The generation of pulsating compressed air by the pump according to the invention proves to be very practical here since the paper edges can be separated more easily by means of the pulsating compressed air that is generated. Negative pressure is required in such applications to pick up the top sheet of paper.
In the preferred embodiment of the pump, the rotors, together with the pump chamber, define a suction cell that is connected to the suction port and whose volume increases during the rotation of the rotors and they also define a pressure cell whose volume decreases when the rotors rotate and that is connected to the pressure port. This pressure cell is comprised of two charging cells that are initially separated from each other during the rotation of the rotors, whereby these charging cells each have an associated charging port and that, during the further rotation of the rotors, are united with each other to define the pressure cell. Before being united, the charging cells are moved essentially isobarically and isochorically in the pump chamber, that is to say, the air present in the charging cells essentially does not undergo any change in pressure or volume during the shift of the charging cells.